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Powder Enameling Defects

Typical appearances and possible cause

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" It is a paradox of the porcelain enameling industry
that it is less expensive to produce good ware
than to produce an equal quantity of bad ware."

Beneath you will find a comprehensive outline of major enamel defects and their possible causes,
which is mend to simplify troubleshooting your enameling operation.


Related Links

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enamel equipment
enameling plants
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enamel technology

Defect Appearance Possible causes
Back-ionization Localized heavy orange peel + Excessive film thickness
+ Too high gun voltage
+ Guns too close to work piece
+ Low relative humidity of ambient
+ Poor earthing
+ High powder receptivity
+ No AFC used
Black specks Blisters or circular holes + Iron contamination
+ Poor steel quality
+ Over pickling
+ Contamination with organic materials
+ High humidity in furnace
+ Incompatible enamel combination (2c/1f processes)
Chrome contamination Black specks
enclosed in a yellow halo		 + Scaling from firing tools
+ Scaling from furnace furniture
Dimples Slight depressions
in enamel surface		 + Oil or water spots from compressed air line
+ Contamination by dust from ambient
+ Contamination by sulphate depositions
Faraday cage Burning off due to thin spraying
in the angle of sharp corners		 + Too high charging potential (kV)
+ Poor product design
+ Poor particle size distribution of enamel
+ Excessive amounts of reclaimed enamel
Gun spitting Raised areas,
sometimes discolored		 + Powder accumulation around gun tip
+ Poorly maintained guns
+ Using compressed air with too high dew point
Poor powder adhesion Localized fall off of powder + Poor powder charging
+ Too many large powder particles
+ Poor powder storage
+ Too low charging voltage (kV)
+ Excessive gun-to-ware distance
+ Excessive powder recycling
+ Vibrations / shocks
+ Interval between powder application and firing


For more detailed information about enamel defects, I would refer to the excellent manuals of
the American and English Enamel Associations :

- Atlas of enamel defects, VEI, 1996
- Technical manuals, PEI, 1997


and the reference book by Silvano Pagliuca and William D. Faust :

- Porcelain (Vitreous) Enamels and industrial enamelling processes, 2011


About Us

Ditmer Trading & Consulting BV is a family owned company,
which was founded by Ronald Ditmer in 2007.

We are specialized in providing worldwide know-how, technical services
& equipment to the porcelain (vitreous) enameling.

Company details

Ditmer Trading & Consulting BV
Palissander 141
3315MP Dordrecht
The Netherlands

Phone : +31-78-6169877
e-mail : info@ditmer.nl


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